1. Field of the Invention
This invention relates to an image processing apparatus and an image processing method and, more particularly, to an image processing apparatus and an image processing method in which an input image is processed and supplied to an image output apparatus so that the processed image will be output from the image output apparatus.
It also relates to image formation means for forming images onto printing paper through a plurality of previously-assigned, individual processings, a printer provided with control means for controlling the image formation means, and a print control apparatus and a print control method used in the printer.
2. Related Background Art
In the conventional, identical dither matrix and .gamma. correction method are used, regardless of individual conditions, such as the status of a printer engine to be used, the type of image to be output (e.g., character, graphic or bit map image), aged changes, and the type of recording medium.
Therefore, the following problems arise in the conventional.
1) Since information on the printer engine's status is used only for warning to the user, a shortage of toner causes the printer to continuously output faint images with low toner density unless the toner is supplied, for example, by replacing the toner cartridge.
2) Since an identical dither matrix is used regardless of the type of image to be output, the print quality may be lowered depending on the type of image.
3) Since an identical y correction method is used regardless of aged changes, the image quality may deteriorate with the aged changes.
4) Since the identical dither matrix is used regardless of the type of recording medium, there may occur inconvenience to use. For example, the use of an OHP sheet as the recording medium causes low transmittance.
Generally, printers are classified into various types such as ink-jet type, thermal transfer type, and electrophotographic type. For example, the electrophotographic type includes laser beam printers.
Such printers typically have image formation means (hereinafter, referred to as a printer engine) for forming images onto printing paper through a plurality of previously-assigned, individual processings, and control means (hereinafter, referred to as a printer controller) for controlling the printer engine.
Specifically, the printer controller is communicably connected to external equipment such as a host computer, which analyzes print information sent from the external equipment and generates printable image data to be sent to the printer engine. The printer controller also issues control instructions related to the printing to be performed by the printer engine.
The printer engine prints out the image data sent from the printer controller in accordance with the control instructions from the printer controller. All the processing to be performed in this printing process, such as paper feeding and printing, is controlled by an engine control unit.
Referring to FIG. 23, a laser beam printer will be taken from the above printers by way of example to describe a configuration of a printer controller and a printer engine. FIG. 23 is a block diagram showing a configuration of a printer controller and a printer engine in a conventional laser beam printer.
As shown in FIG. 23, the conventional laser beam printer includes a printer controller 501 and a printer engine 502.
The printer controller 501 is communicably connected to external equipment (not shown) such as a host computer so that instructions and responses can be exchanged therebetween. The printer controller 501 also performs the following processing steps of: receiving print information from the external equipment; analyzing the received print information to expand it into printable image data; transferring the image data to the printer engine 502; and exchanging instructions and responses with the printer engine 502 connected to the printer controller 501 through a serial communication line.
The printer engine 502 prints out the image data sent from the printer controller 501 in accordance with control instructions from the printer controller 501. All the processing to be performed in this printing process is controlled by an engine control unit 503.
Control processing by the engine control unit 503 includes paper feeding control processing of printing paper; paper conveying control processing of the printing paper; control processing in an optical system, including control processing to drive a scanner motor and laser light used for forming an electrostatic latent image onto a photoconductive drum; temperature control of a fixing device for fixing a toner image transferred onto the printing paper; and other control processing in the fixing device including temperature abnormality detection.
In the paper feeding control processing of the printing paper, the type and the size of feedable printing paper, and the presence or absence of such feedable printing paper are detected on the basis of detection signals from a paper size detecting unit 403, a paper detecting unit 404 of a paper feeding unit, and an option detecting unit 405, respectively. Then a cassette or an option control unit 409 is instructed to feed printing paper of the designated type and size.
The paper size detecting unit 403 detects the size of the printing paper within a paper cassette currently set to output a detection signal indicative of the detection result. The paper detecting unit 404 of the paper feeding unit detects the presence or absence of respective paper feeding ports of the cassette, a hand feeder, an option cassette, and an envelop feeder, to output detection signals indicative of the detection results. The option detecting unit 405 detects the connecting status of options of the option cassette and the envelop feeder to output detection signals indicative of the detection results. The option control unit 409 instructs the options of the option cassette and the envelop feeder to operate in accordance with control instructions from the engine control unit 503.
In the paper conveying control processing of the printing paper, control instructions are issued to a paper conveying control unit 406 to convey the printing paper along a required conveying path on the basis of detection signals from a sensor input unit 410 that detects the presence or absence of the printing paper within conveying paths for registration, paper ejection, both-side printing and reversed printing. The paper conveying control unit 406 instructs conveying motors to drive conveying rollers, arranged in the respective conveying paths, in accordance with the control instructions from the engine control unit 503.
In the optical system control processing, status signals indicative of the status of the optical system are taken in from an optical system control unit 407, and control instructions to the optical system control unit 407 are generated on the basis of the status signals. The optical system control unit 407 instructs drivers for a scanner motor and a laser to operate in accordance with the control instructions from the engine control unit 503.
In the fixing device control processing, a status signal is taken in from a fixing device temperature control unit 408, the temperature of the fixing device is monitored on the basis of the status signal, and a control instruction is issued to the fixing device temperature control unit 408 to control a heater of the fixing device to be a fixing temperature within a predetermined range. When detecting occurrence of abnormality such as temperature abnormality due to a trouble in the heater of the fixing device, a control instruction is generated to stop operation of the fixing device. The fixing device temperature control unit 408 instructs the source of trouble such as the heater of the fixing device to operate in accordance with the control instruction from the engine control unit 503.
The engine control unit 503 executes all the control processing on the basis of signals exchanged with the printer controller 501. Such signals includes those denoted in FIG. 23 as /CPRDY411, /PPRDY412, /RDY413, /PRNT414, /VSREQ415, /VSYNC416, /BD417, /SCLK418, /CMD419, /CBSY420, /STS421, and /SBSY422.
The signal /CPRDY411 indicates that the printer controller 501 is in a communicable state to the engine control unit 503. The signal /PPRDY412 indicates that the engine control unit 503 is in a standby state in which the engine control unit 503 is communicable with the printer controller 501.
The signal /RDY413 is a signal indicating whether or not the engine control unit 503 is in a standby state in which the engine control unit 503 maintains a printable state. This signal is set to "TRUE" when the status of all the processing in the printing process satisfies preset conditions, or to "FALSE" when the status of all the processing in the printing process does not satisfy the preset conditions, i.e., when the engine control unit 503 is in an abnormal state in which the printing process can not be executed normally.
The signal /PRNT414 indicates that the printer controller 501 requests the engine control unit 503 to start printing. The signal /VSREQ415 indicates that the engine control unit 503 requests the printer controller 501 to generate a vertical synchronizing signal. The signal /VSYNC416 is the vertical synchronizing signal that is output from the printer controller 501 to the engine control unit 503 in response to the signal /VSREQ415. The signal /BD417 is a horizontal synchronizing signal that is output from the printer controller 501 to the engine control unit 503. The signal /SCLK418 is a synchronizing clock signal for synchronizing serial communication between the printer controller 501 and the engine control unit 503.
The signal /CMD419 is a command signal sent from the printer controller 501 to the engine control unit 503. The signal /CBSY420 is a strobe signal for outputting the signal /CMD419. The signal /STS421 is a signal output in response to the signal /CMD419, indicating the internal status of the printer engine 502. The signal /SBSY422 is a signal for outputting the signal /STS421.
A description will be made next to how the printer controller 501 controls the printer engine 502.
The engine control unit 503 performs printing under control of the printer controller 501. If the printing process is executable normally, the /RDY signal of "TRUE" is output. If not executable, i.e., when an abnormal state such as a paper jam occurs and it requires the engine control unit 503 to stop printing, the /RDY signal of "FALSE" is output.
The printer controller 501 monitors the signals /RDY413 and /STS421 from the engine control unit 503, and recognizes a change in status of the printer engine 502 to control the printer engine 502 in accordance with the change in the status. For example, when the /RDY signal is "FALSE", the /RDY signal is used as a trigger signal to detect occurrence of abnormality in the printer engine 502 (e.g., paper jam), and the signal /CMD419 is output to the printer engine 502 so that the current processing will be stopped.
On the other hand, the signal /STS421 in each processing is read out by polling or the like, and a status change that does not directly concern the /RDY signal is recognized by the signal /STS421. When occurrence of an error in the printer engine 502 is detected through the recognition of the status change, the signal /CMD419 is output to the printer engine 502 so that the current processing will be stopped.
The engine control unit 503 controls the printer engine 502 to stop all the processing in the printing process in response to input of the signal /CMD419. The printer engine 502 maintains the stop state until either the /RDY signal is recovered from the "FALSE" state to the normal "TRUE" state, or elimination of the error is detected by the signal /STS421.
When the occurrence of the error is detected by the signal /STS421, the engine control unit 503 can control the printer engine 502 to skip the processing in which the error occurs, so that the printer engine 502 advances the subsequent processing without stopping the operation.
As previously described, according to the conventional control method, when occurrence of an abnormal state of the printer engine 502 such as a paper jam is detected by the /RDY signal from the engine control unit 503, the printer controller 501 instructs the printer engine 502 to stop the processing on purpose to deal with the occurrence of the abnormal state. Therefore, unsuitable printout can be prevented. Similarly, when occurrence of an error in a state that does not directly concern the /RDY signal is detected by the signal /STS421 in each processing, the printer controller 501 instructs the printer engine 502 to stop the processing regardless of contents of the error on purpose to prevent unsuitable printout. In this case, the processing to deal with the occurrence of the error in the state that does not concern the /RDY signal is determinate and cannot cope with the occurrence of the error flexibly. In other words, the processing to deal with a status change due to the occurrence of the abnormality or error in the printer engine 502 is determinately executed to stop the processing in the printer engine 502, and cannot cope with the occurrence of the error in the printer engine 502 flexibly.
Further, since error detection in the state that does not directly concern the /RDY signal is done on the basis of the signal /STS421 in each processing, the signal /STS421 always needs to be read out by polling and this causes an increased load on the printer controller 501.